It has long been known that a magnetoresistive element, commonly used to read magnetic information from a track written onto a magnetic media, could be used in a center-tapped configuration to control the position of the entire magnetic head with respect to the information track that the MR element is following, see U.S. Pat. No. 3,918,091 to Walraven, et al. The difference of the voltages across each outside conductor and the center conductor is said to be indicative of the position of the head. The U.S. Pat. No. 4,633,344 shows a center-tapped MR element for providing a tracking servo signal using the signals derived from the data on the track. This patent discloses a particular circuitry for differentiating between the servo signal and the data signal itself. The center-tapped MR sensors provides an excellent means of getting away from the traditional servo system where the positioning servo information is recorded on a separate, dedicated disk surface in the disk stack or the problems encountered by embedding the servo information on the track on which the head is used, such as a sector servo with microsectors. The sector servo information takes up disk space which could otherwise be used for storing data, thus making it impossible to have continuous feedback of position error signal during reading and writing. The center-tapped MR sensor solved this problem by deriving the position servo signal directly from the actual data. The straight forward design of adding a center-tap lead connection to the center of the MR transducer resulted in problems. The conductor pad at the center of the MR sensor disturbed the magnetic bias and shorted out the center portion of the sensor. This made the center-tapped MR sensor incompatible with narrow track applications. A three terminal MR transducer design with the aim of removing the dead center at the center of the MR sensor is described in U.S. Pat. No. 4,012,781 to Lin and assigned to the assignee of the present invention. The head actually included two MR sensing elements separated by an insulating layer. The center conductors are positioned such that the active regions of the two MR sensors line up to form one continuous active region. Besides additional process steps required to make the two separate elements, the design has a few limitations solved by the present invention. First, since the position servo signal is derived as the difference of the output of the two MR sensors, to give a zero difference signal when the head is on track, the sensitivity of the two MR sensors must be equal. This is difficult to accomplish since the two MR sensors are fabricated at different steps and therefore allowances must be made in the circuitry to allow for the differences. Second, if the magnetic head is also used to read data, the phase lag between the outputs of the two MR sensors must be accommodated in the circuitry since the sensors are each reading a portion of the data at a slightly different time, depending on the thickness of the insulating layer and the velocity of the disk media.
It is, therefore, an object of the present invention to provide an MR sensor with a center tap that overcomes the disadvantages of the prior art.
Another object of the present invention is to provide an MR sensor that includes a center tap in order to servo on the data that does not degrade the sensitivity of the MR sensor.
A further object of the present invention is to provide a center tap MR sensor wherein the center tap is self aligned to the outer conductors and the two sections of the MR sensor are thereby identical in physical as well as magnetic properties.